The present invention relates to a tire inspection apparatus and methods to such apparatus which are particularly suited to the tire retreading industry.
Various types of x-ray equipment have been used in the past for the inspection of tires to discover defects not visible by the naked eye. For the most part, such apparatus have been associated with automotive servicing or the maintenance of tires. Apparatus installed in service stations and tire retailers are usually adapted for inspection of tires which are mounted on rims for the discovery and location of defects incurred in the use of the tires on the road so that the defects can be repaired or the tire replaced before a blowout endangers life. In the tire manufacturing business, tire makers universally use x-ray apparatus for quality control purposes to discover manufacturing defects.
In trucking operations involving medium and large trucks, it is a standard practice to recap or retread tires after a period of use in which the original tread has worn away. The reason for this is simple: the cores of medium and large truck tires are relatively expensive. In most cases, little damage of a non-repairable nature occurs to the core (referred to as a coram once the tread is worn away) of truck tires in normal use such that the tires can be safely retreaded if substantially undamaged tire carcasses are reused. On the other hand, when a carcass with structural defects is retreaded, the tire can be completely destroyed under the pressures and temperatures which occur during normal use. Such failures can create hazards to the driver and others on the road, as well as causing expensive down time for the truck and cargo. Visual inspection does not always indicate if a tire carcass has been damaged. While large punctures and damage to the rubber portions of a tire can often be found by visual inspection, small punctures and damage, especially to the tire cords or belts are not usually visible externally.
The hazards to humans from overexposure to penetrating radiation, such as x-rays, are more fully appreciated in current times than in the past. Thus, while various types of x-ray apparatus for general and specialized tire servicing establishments have been proposed, such apparatus is not in general use at this time because of the need to provide specialized training to infrequent operators of such equipment, the expense of purchasing and maintaining such equipment, and the potential liabilities involved. In contrast, quality control and product liability concerns in tire manufacturing require that newly manufactured tires be closely inspected. Since x-ray inspection of tires in such manufacturing settings is an ongoing operation, the expense of x-ray equipment and the training of personnel can be more easily justified. As a result, the development and availability of industrial tire x-ray equipment has continued while the development and availability of similar equipment suitable for small commercial operators has lagged.
For safety reasons, it is necessary to inspect both sidewalls and the tread of a tire. Conventionally, testing equipment has either included multiple x-ray sources and image intensifiers to simultaneously x-ray both sidewalls and the tread of a tire, or the tire has been physically removed from the inspection equipment and reversed, which is time consuming and labor intensive. Applicant has addressed certain of the concerns of the industry in his previous U.S. Pat. Nos. 4,839,914 and 4,977,586 which are incorporated herein by reference. However, certain problems were not fully resolved by the devices disclosed in the two prior patents.
In particular, U.S. Pat. No. 4,839,914 is directed to a portable tire x-ray inspection device which has a single x-ray source and image intensifier which is mounted in a fixed position with respect to a tire being inspected. The tire is mounted on a platform which has a plurality of rollers which rotate the tire and permit one entire sidewall to be examined without physically moving the x-ray apparatus. While this arrangement was an improvement, it did not solve the problem of the operator having to physically remove and reverse the tire in order to inspect the opposite sidewall.
U.S. Pat. No. 4,977,586 was an improved portable x-ray inspection apparatus which mounts the x-ray source and the image intensifier on a wheeled carriage which permits it to be rotated around the tire so that both sidewalls of the tire can be inspected without physically removing the tire from the apparatus. This arrangement has proven to be satisfactory except that the x-ray apparatus and image intensifier must be physically swung around the tire which means that the operator must leave his shielded environment both to mount the tire for inspection of a first sidewall and again to swing the x-ray apparatus about the tire to inspect the opposite sidewall.
Another problem which is not addressed by the above-cited patents is that a tire can be much more reliably inspected if the tire sidewalls are spread apart during inspection. A normal truck tire in an unspread condition will have the radially inner edges of the sidewalls spaced closely together, for example, approximately 2"-4". This relatively small spacing does not leave enough space to position an x-ray source relative to the tire without some distortion. This means that x-rays must penetrate a portion of the near sidewall and then the subject opposite sidewall before reaching the image intensifier. This decreases the quality and reliability of the resulting analysis and can even cause invalid results if a defect is located near the edge of the near sidewall, but is attributed to the subject opposite sidewall. Furthermore, the tread cannot be reliably inspected if the x-ray source cannot be inserted in between the sidewalls.
It is clear, then, that a need exists for a portable tire x-ray apparatus which can spread the sidewalls while rotating a tire to be inspected and which can automatically swing the x-ray source and image intensifier relative to the tire so that an operator can inspect a tire without leaving a shielded environment, thereby also reducing the time required to inspect each tire.